Cereals constitute a major part of the human diet and are an important source of starch and dietary fiber. In the preparation of cereals for human consumption high temperature-short time extrusion cooking is widely used. The food products prepared by extrusion techniques are typically ready-to-eat cereal and snack foods, crisp breads, pasta and noodles. Research literature has indicated that the inclusion of fiber into human diets is beneficial, and as a result, there have been attempts to fortify extruded foods with dietary fiber. Nevertheless, it has proven difficult to make a satisfactory food product that has high fiber content through extrusion techniques.
The quality attributes of extruded food products pertain mainly to their texture and crispness, which in turn relate to their expanded volume and bulk density. It is known that extrusion processing variables, such as, barrel temperature, screw configurations, nozzle size and shape, screw speed, and moisture content prior to thermal processing, can influence the expansion volume of the extruded product. The protein, lipid, and starch content of the raw materials for making the dough mix also affect the texture and expansion volume of extruded foods.
In U.S. Pat. Nos. 5,169,662 and 5,176,936, it is disclosed that products with significant amounts of dietary fiber are difficult to expand. Expansion is critical in certain extruded foods because the crispness and texture of the foods is related to expanded volume and bulk density. It is also difficult to obtain good or acceptable texture in flaked products or in pasta and noodles when those products are fortified with high fiber because the addition of dietary fiber adds density and reduces favorable texture and overall eating quality.